1. Field of the Invention
Exemplary embodiments of the present invention relate to a packet transmission/reception method and apparatus in a wireless communication system.
2. Description of Related Art
The throughput of wireless communication systems is not high enough to support various high-capacity multimedia services. Since multi-users share wireless resources, the data rate of wireless services sensed by the users decreases remarkably. In this regard, research is conducted on various techniques to improve the throughput of a wireless communication system for multi-users by increasing a bandwidth to expand wireless resources shared by multi-users, or by implementing a desired beam for communication with each user while using wireless resources of the same bandwidth.
Since a medium access control (MAC) protocol of a wireless communication system operates on the basis of carrier sense multiple access/collision avoidance (CSMA/CA), resource waste may occur in a channel contention process. In order to solve such a problem, an enhanced MAC protocol defined by IEEE 802.11e has proposed a burst transmission scheme in which multiple MAC protocol data units (MPDUs) are transmitted at a short inter-frame space (SIFS) during a transmission opportunity (TXOP) time when a transmission right for a wireless resource is acquired, and block ACKs for the multiple MPDUs are received. Furthermore, IEEE 802.11n has defined an aggregated MAC service data unit (MSDU) (hereinafter, referred to as A-MSDU) and an aggregated MPDU (hereinafter, referred to as A-MPDU). In this case, MSDUs and MPDUs (which are a transmission unit) may be respectively aggregated without IFS, and then transmitted through a one-time contention process for a wireless resource.
With the development of the above-described wireless communication system, IEEE 802.11ac specifies that, in order to construct a high-rate wireless communication system, a data rate of up to 1 Gbps should be supported by a MAC service access point (SAP) of an access point (AP) in a wireless communication system including one AP and two stations (STAs), and a data rate of up to 500 Mbps is required by a MAC SAP of an STA for a point-to-point environment. Furthermore, as the requirements of the high-performance wireless communication system, each AP and STA need to support compatibility with the existing wireless communication system (the IEEE 802.11a/n system).
In the wireless communication system, a data transmitter (AP or STA) acquires a wireless channel and then transmits data together with information required for the transmission of the data. A structure including the data and the information required for the data transmission may be referred to as a packet. At this time, the information required for the data transmission is defined as a promised value in a structure named ‘header’.
FIG. 1 illustrates the structure of a packet defined in IEEE 802.11a. A protocol header and data information of a previous stage, for example, a MPDU with a header and data of a MAC protocol is transmitted to a receiver, together with short and long training fields 110 and 120 storing information required for a physical layer (PHY), a signal field 130, a service field 142, and a tail & padding field 144, and the receiver receives the data using information acquired from the received fields. At this time, the data included in a data field 140 as well as the service field 142 and the tail & pad field 144 has a variable length within the maximum range. It is possible for the receiver to recognize the length of the data through information stored in a length field 132 of the signal field 130.
FIG. 2 illustrates the structure of a packet with a mixed format, which may be received both in an IEEE 802.11a system and an IEEE 802.11n system. Referring to FIG. 2, as the packet with a mixed format includes legacy fields 210 such as a legacy-short training field (L-STF), a legacy-long training field (L-LTF), and a legacy-signal field (L-SIG), the IEEE 802.11a system may acquire information required for the reception of data. Furthermore, the packet includes fields 220 for the IEEE 802.11n system from an HT-SIG field such that the IEEE 802.11n system may acquire information required for the reception of data. For example, the IEEE 802.11a system uses length information stored in the L-SIG field, and the IEEE 802.11n system uses length information stored in the L-SIG field or information stored in a length field 222 in the HT-SIG1, thereby recognizing the length of data.
As the packet structures as illustrated in FIGS. 1 and 2 are defined in the IEEE 802.11a and 802.11n wireless communication systems, there is a demand for a packet structure suitable for a high-performance wireless communication system (e.g., a wireless communication system based on multi-user multi-input multi-output (MU-MIMO) technology), which is capable of simultaneously transmitting different packets to multi-users, respectively.